It is known in the photographic arts that photographic elements can produce dye images through the selective formation of dyes. It is also known that the dyes can be formed by reacting (i.e. coupling) a color-developing agent such as a primary aromatic amine in its oxidized form, with a dye-forming coupler. It is also known that pyrazolotriazoles constitute one type of dye-forming coupler which can form subtractive primary (yellow, magenta, and cyan) image dyes.
Because of the utility of pyrazolotriazoles as dye couplers, new pyrazolotriazole starting materials, and new processes for preparing them are always of interest in the art.
In the course of work conducted in connection with the development of this invention, an attempt was made to synthesize 1-acetyl- [6-methyl- 3-[3-(4-nitrophenyl) propyl]-1H-pyrazolo[5,1-C]-1,2,4-triazole, by acetylation of 6-methyl-3-[3-(4-nitrophenyl) propyl]-1H-pyrazolo[5,1-C]-1,2,4-triazole in boiling acetic anhydride. Surprisingly, it was found that the pyrazolotriazole acetylated at the 7-carbon, as well as at the 1-nitrogen. An attempt was made to repeat this unexpected reaction using 6-methyl-3-[3-(4-nitrophenyl) propyl]-1H-pyrazolo[5,1-C]-1,2,4-triazole prepared by another method. The results were different, i.e. the diacetylation was not repeated, only monoacetylation occurred. Further experimentation showed that the 1,7-diacetylation requires the presence of an acid catalyst.
Thus, it appears (a) that the 6-methyl-3-[3-(4-nitrophenyl) propyl]-1H-pyrazolo[5,1-C]-1,2,4-triazole which gave the diacetylation contained a catalytic amount of an acid catalyst, (b) that this acid catalyst was introduced during preparation of the pyrazolotriazole, and (c) that it therefore yielded the 1,7-diacetyl product without the addition of more acid.
Subsequent work has also showed that the 1,7-diacetyl compound is a valuable intermediate for the preparation of other triazoles. Such use of the 1,7-diacetyl compound and related compounds is discussed and exemplified below, and constitutes part of this invention.